Transformations for Antlr grammars

At this point, I am working on the code for refactoring Antlr grammars in Antlrvsix. While I plan to use Piggy to implement these refactorings, I will first implement them in C# code so I can get a clear picture of what to do with Piggy, make any changes, then rewrite the refactorings using Piggy templates.

1/2: Adding to #Antlrvsix an analysis tool of #Antlr grammars. This is how it works with cycle detection and useless lexer rules. There are some issues in the responsiveness of the MS LSP client for VS2019.

Adding to #Antlrvsix the refactoring to remove useless parentheses in an #Antlr grammar. This is how it works with the extra parentheses in the arrayAccess_lf_primary rule in Java9.g4 that nobody knew were there. Only yet starting to scratch the surface of grammar optimizations.

Implementing #Antlr grammar fold refactorings in #Antlrvsix. Two types: extract a selected sequence of symbols and make a rule (shown first); replace all occurrences in the grammar with a folded rule (shown second). Spacing and comments do not matter.